1. Field of the Invention
The present invention relates to a surface emitting laser device and a method of manufacturing the surface emitting laser device.
2. Description of the Related Art
A vertical cavity surface emitting laser (surface emitting laser, hereinafter, “a surface emitting laser device”) is used as a light source for optical communications such as an optical interconnection or a device for various applications. A plurality of surface emitting laser devices can be arranged in a two-dimensional array on a single substrate more easily than edge-emitting laser devices, because each surface emitting laser device emits a laser light in the vertical direction with respect to the substrate. Moreover, the surface emitting laser device has preferable properties, due to a small volume active layer, such as extremely low threshold current and laser oscillation at low consumption power.
In a typical surface emitting laser device, a distributed Bragg reflector (DBR) mirror, which is a multilayer mirror, is used in a resonator. It has been widely known that a dielectric DBR mirror as a dielectric multilayer mirror can reduce optical absorption loss, so that it is possible to obtain a high-power laser source, and there have been developed surface emitting laser devices including the dielectric DBR mirror in a resonator (see, for example, U.S. Pat. No. 6,185,241).
FIG. 6 is a cross section of the surface emitting laser device disclosed in U.S. Pat. No. 6,185,241. In the surface emitting laser device shown in FIG. 6, a light generated by an active layer 21 based on an injected current is resonated between a lower DBR mirror 22 and an upper DBR mirror 23, and is emitted as a laser light from an exit surface 23a on the upper DBR mirror 23. A spatial filter layer 24 is provided between the lower DBR mirror 22 and the upper DBR mirror 23. The laser light emitted from the exit surface 23a is diffracted by the spatial filter layer 24, and is transmitted through the upper DBR mirror 23 at a spreading angle (diffraction angle) depending on the diffraction.
In the surface emitting laser device shown in FIG. 6, an exit aperture 24a for forming a concave-shaped space is formed on a center portion of the spatial filter layer 24. The upper DBR mirror 23 is formed on the spatial filter layer 24 in the above state, so that a concave portion 23b is formed, along the concave shape of the exit aperture 24a, in the upper DBR mirror 23 above the exit aperture 24a. With this configuration, a marginal ray 25 of the laser light that has passed through the exit aperture 24a is scattered by a side-wall portion (tilt portion) of the concave portion 23b, which disadvantageously causes an optical intensity loss. Moreover, the scattered marginal ray causes disturbance in a Far Field Pattern of the laser light that is emitted from the exit surface 23a. 